‘I contain multitudes,” the poet Walt Whitman famously wrote. n Of course, Whitman never met Jefferson Mays, else he might’ve felt that his own multitudes seemed minuscule. n Then again, there’s nothing especially contained about the characters that come spilling out of Mays when this UC San Diego-trained, Broadway-seasoned actor hits the stage. n Mays is now peopling no fewer than eight roles — both male and female — in the Old Globe Theatre’s world-premiere musical comedy “A Gentleman’s Guide to Love and Murder.”

That tally actually was dwarfed by the 40-some characters he portrayed in “I Am My Own Wife,” the solo play in which Mays starred at La Jolla Playhouse and then on Broadway, winning a Tony Award in the process.

But more than mere numbers, it’s the sense of whimsy and idiosyncrasy that Mays brings to both life and work that seem to predispose him to stepping into a whole chorus line of other people’s shoes.

“He is an eccentric,” as Globe artistic director Barry Edelstein says of the actor. “His own sensibility as a man matches the kooky world of the play in a remarkable kind of way. I think that’s the X-factor that (audiences) are responding to.”

“Gentleman’s Guide” centers on an everyday Englishman (played by Ken Barnett) who learns he is ninth in line for a royal title. Lacking the good manners to just let those ahead of him keel over naturally, he decides to speed up the process by offing them in various inventive ways.

Mays plays all those unfortunate (although largely insufferable) souls, which makes his blizzard of costume and character changes something like a track meet or, as Edelstein describes the backstage scene, like the pits at a NASCAR race.

Mays talks of such job hazards as “mustaches getting glued to the soles of shoes.” But he says it’s all been getting smoother, given that this is actually the show’s second run: “Gentleman’s Guide” first went up late last year at Hartford Stage, which is co-producing the piece and is the artistic home of director and former Globe resident artistic chief Darko Tresnjak.

In conversations during Globe rehearsals and over the phone, Mays chatted about the show, his San Diego past, and how making theater can prove a slippery slope.

Q: Between the Hartford production and now the Old Globe’s, have you been able to figure out some shortcuts to make this whole flurry of character changes work?

A: Yeah, you discover them in the playing. Each theater is different, of course. It’s nice to be doing it in this climate, I must say, because I can literally run outside (through a backstage door) into the cool of the evening for a little cool-down. I live in terror, of course, of locking myself out. But I think if they could hear my agonized pounding, they’d let me back in. And it’s becoming quite the ballet with my dressers. We had to have special costume-change rehearsals. I didn’t really have any skin left on my body during tech (rehearsal) after that. But now we have it down, and I feel as though I have time for a cigarette. But we mustn’t get too smug or cocky about it, or something horrible will happen.